The invention relates to a control device for an exhaust gas guide section of a turbine of an exhaust gas turbocharger with a control arrangement for opening and closing a turbine bypass duct.
Publication DE 11 2009 002 230 T5 shows a control device for an exhaust gas guide section of a turbine, in particular for a turbine of an exhaust gas turbocharger. The control arrangement is provided for opening and closing of a bypass duct in the flow-through exhaust gas guide section for bypassing a turbine wheel which is rotatably arranged in a turbine wheel chamber of the exhaust gas guide section. The control device comprises an actuating device and a cover element, with the actuating device being provided for moving the cover element. The cover element serves for opening or closing a flow cross-section of the bypass duct by means of a translatory motion of the cover element. With such a control device, it is possible to bypass the turbine wheel completely or partially under certain operating conditions of the exhaust gas turbocharger, in particular at operating conditions with large flow volumes, so that a more efficient operation of the exhaust gas turbocharger may be realized. In its simplest configuration, the cover element has e. g. the shape of a plate.
A basic problem with these control devices which are generally referred to as waste gates, is that flow disturbances and noise emissions occur upon opening or closing of the flow cross-section by means of the cover element, which noise emissions cannot necessarily be decoupled from flow disturbances. The term flow disturbances as used herein refers to deviation of the flow from a substantially uniform or linear flow. Such deviations may result both from the operation of a combustion engine which is usually connected with the exhaust gas turbocharger due to the pressure pulsations upon opening and closing of valves of the combustion engines or from opening of the flow cross-section due to a sudden release of the flow cross-section of the bypass duct.
The cover element performs an axial motion in the bypass duct, which is initiated by means of the actuating device. The cover element is usually not rigidly connected with the actuating device. If the cover element were rigidly connected with the actuating device this would mean that the actuating device itself is configured to perform an exclusively axial motion. Usually, the actuating device together with the cover element performs translatory and rotatory motions which can be effected by means of several articulated joints. Because articulated joints are not rigid connections, but are principally built with a certain degree of play, in particular flow-induced pulses acting on the control apparatus may produce noises such as e. g. rattling, which is caused by bumping of the cover element against a casing wall.
The publication shows a cover element which is concerned with the problem of exposure of the cover element to a non-linear or turbulent inlet flow. The cover element of the control device comprises a horn for influencing the flow, wherein the horn is formed as a three-dimensional extension of the cover element in a direction towards the exhaust gas flow. The horn is formed to generate a progressive unblocking of the flow cross-section upon opening.
It is the object of the present invention to provide a control device for an exhaust gas guide section of a turbine by means of which a reduction of noise emissions with a simultaneous compensation of a non-linear flow for the reduction of flow losses can be accomplished.